Questions linger about dolphin recovery in eastern tropical Pacific

Calls mount for research voyage to find status of populations

A school of eastern spinner and spotted dolphins swims at the surface in the eastern tropical Pacific. These dolphins, seabirds, and yellowfin tuna form multispecies groups that are a hallmark of the eastern tropical Pacific Ocean and the basis of one of the world's largest tuna fisheries
— Southwest Fisheries Science Center/National Marine Fisheries Service

A school of eastern spinner and spotted dolphins swims at the surface in the eastern tropical Pacific. These dolphins, seabirds, and yellowfin tuna form multispecies groups that are a hallmark of the eastern tropical Pacific Ocean and the basis of one of the world's largest tuna fisheries
/ Southwest Fisheries Science Center/National Marine Fisheries Service

At the tuna commission, Hall also wants to see another months-long federal dolphin survey because he’s confident it will confirm an upward swing in the numbers and allow his agency to focus on what he sees as more pressing issues such as sea turtle conservation.

Cisco Werner, head of the Southwest Fisheries Science Center, couldn’t give specific dates for the next journey to the eastern tropical Pacific because it will depend on ongoing budget negotiations and priorities set across the National Oceanic and Atmospheric Administration

“The Southwest Fisheries Science Center is committed to maintaining a research program focused on the eastern tropical Pacific where we have monitored the recovery of cetacean species and other ecosystem components for decades,” Werner said.

Despite those intentions, the growing data gap is a point of concern inside the agency and elsewhere.

“Whenever we deplete a population like this, we have a responsibility to make sure the populations are recovered to the best of our ability,” said Timothy Ragen, executive director of the U.S. Marine Mammal Commission, an independent agency that oversees federal efforts. “To not do the science would be a real shortcoming.”

Dolphins and yellowfin tuna are tightly connected in the eastern tropical Pacific, a roughly triangular region larger than Africa that stretches from Tijuana south to Peru and east to Hawaii.

The fish and the marine mammals swim together in large schools, a phenomenon that isn’t as pronounced in other parts of the world’s oceans. One theory is that the relatively shallow colder water of the region pushes tuna toward the warmer surface layer and puts them close to dolphins.

The commingled schools are a boon for fishermen because dolphins provide a clear visual cue that yellowfin are near. In the 1950s, the development of synthetic netting and hydraulics capable of hauling huge purse-seine nets with tons of tuna inside enabled the commercial industry to flourish with San Diego as a hub.

Fishermen started using a technique called “dolphin sets” in which they would use speedboats to chase dolphin and tunas a tight group and set a purse-seine net around them. As the nets were pulled closed, dolphins died by the droves because they couldn’t surface for air. U.S. consumers went wild when they learned the charismatic creatures — made famous by TV shows such as “Flipper” — were drowning by the hundreds of thousands.

By the early 1990s, new techniques were adopted by many in the tuna industry and dolphin deaths in the eastern tropical Pacific plummeted to roughly 1,000 a year. Federal data show that about 99 percent of captured dolphins are released from the nets alive.